This invention relates to the field of microbiological testing.
Many conventional systems exist for performing tests on microbiological samples related to patient diagnosis and therapy. The microorganism samples may come from a variety of sources, including infected wounds, genital infections, cerebro-spinal fluids, blood and abscesses. From those microorganism samples an inoculum is prepared in accordance with established procedures which produce a bacterial or cellular suspension of a predetermined concentration. Further processing of the suspension may depend on the testing method employed.
These systems-are used, for example, for identification of which microorganisms are present in a patient's sample. Typically, in such systems, reagents are placed into cupules, or test wells, of identification trays, which in the presence of an actively growing culture of microorganisms change color. Based on the color change, or lack thereof, the microorganism can be identified by the use of reference tables.
Other systems have been developed for susceptibility testing of microorganisms. These systems are used to determine the susceptibility of a microorganism in a sample to various therapeutics, such as antibiotics. Based on these test results, physicians can then, for example, prescribe an antimicrobial product which will be successful in killing or inhibiting the microorganism. In particular, qualitative susceptibility testing produces an indication of whether a microorganism is resistant or sensitive to a particular antibiotic, but does not provide an indication on the degree of sensitivity or resistance of the microorganism. On the other hand, quantitative susceptibility testing, provides an indication of the concentration of the antimicrobial agent needed to inhibit growth of the microorganism. The term minimum inhibitory concentration (MIC) is used to refer to the minimum concentration of the antimicrobial agent that is required to inhibit the growth of the microorganism.
The systems have certain drawbacks. For example, when performing identification and susceptibility testing, the test trays are incubated at a controlled temperature for an extended period of time. At predetermined time intervals, the wells of the test trays are individually examined for an indication of color change or other test criteria. This can be a long and tedious process if done manually by a technician. In addition, the incubation times for identification and susceptibility test trays may differ, or the optimal time to read a test result from the test tray may not be known in advance. Thus, a technician would need to read and record results for a specimen at several different times, sometimes long apart, which may cause assignment or correlation errors.
Automated systems are desirable in performing these tests to minimize the technician handling time, as well as to minimize the possibility of human error. In addition, automated systems that obtain results rapidly and accurately are preferred.
In this regard, a microbiological testing apparatus for the automatic incubation and reading of microbiological test trays is known. The test trays of this apparatus have a plurality of wells which contain the samples or agents to be tested. The trays are first placed in an incubator for a predetermined amount of time. The test trays are then moved to an inspection station. A light source is disposed above the tray and a pair of video cameras are disposed below the tray at the inspection station. Each video camera takes a video image of an entire tray. The video image signal of the entire tray is sent to an image processor to be analyzed.
The image processor requires uniform lighting over the inspection station. Consequently, the processor records the background light level of each pixel within an area of interest corresponding to each well of the tray to account for variability in the light source. The image processor processes the video image of the tray and determines the number of pixels, for a particular well, whose intensity exceeds a predetermined threshold for that area of interest. If the number of pixels exceeds a predetermined number, a positive result is assigned to that well. The image processor analyzes the binary partial results from the wells to determine the possible identity of the microorganisms. The binary partial results are compared to prerecorded patterns of results for each type of test tray to identify the sample in question.
A microbiological testing apparatus for detecting the presence of a fluorescence emitting reaction resulting from the interaction of a reacting agent and a sample for detection, susceptibility, and identification testing, is also known. In this apparatus, multiple trays having a plurality of test chambers are contained within a carousel. This carousel is rotated to move one of the trays close to a detection area. A positioning mechanism radially then moves that tray out of the carousel and into the detection area. A high-energy light source is disposed proximately to the thus positioned tray. The light source provides narrow-band light sufficient to produce an emission fluorescence from the reaction within test chambers, which in turn is detected by a video mechanism disposed opposite to the light source and behind the positioned tray. The video mechanism produces an image based on the emission wavelength.
Another test system is known for identifying bacteria using signals based on the intensity of monochromatic light reflected from specimens placed in a culture plate having a plurality of cells. A rotary disk containing six interference filters is interposed between a lamp and a group of optical fibers. The light from the lamp passes through a particular interference filter to produce monochromatic light of a certain wavelength. The filtered monochromatic light is guided by the optical fibers to be incident on respective cells of the culture plate. The disk is rotated so that the six different wavelength monochromatic lights are caused to be incident on the cells sequentially. The light reflected from the specimens is guided by additional optical fibers to corresponding phototransistors. A signal is derived for each specimen based on the intensity of the reflected monochromatic light. These signals are then analyzed to determine the identity of the specimen by calculating the difference,-or ratio,-between the signals and comparing that result with a reference value.
However, the above-described apparatuses fail to address all the requirements of a fully automated microbiological testing system. In particular, they are not capable of simultaneously performing both colorimetric- and fluorometric-type testing on multiple-well test panels that is needed to obtain more accurate test results. Further, these apparatuses are generally not designed to continuously gather test data from a plurality of multiple-well test panels in a quick and reliable manner. Moreover, the automated processing of these systems is limited.